CBHVAC wrote:

"RP" wrote in message
...


CBHVAC wrote:


"CJT" wrote in message
...


m Ransley wrote:



Stormin, so cold air is heavier , does my car take more HP to run in
cold air from wind resistance.


It probably does, if that's all you consider. Happily, engines are more
efficient when their intake is cold (plus, you're less likely to be
running the A/C).



On modern vehicles, when you go to WOT, the AC is kicked out...even then,
at highway speeds, less than 2HP is used to run it.

The reason that a car likes cold air is that cold air is more dense.
Helps to slightly increase volumetric efficiency.

The reason that with HVAC issues you have a faster speed on cool than you
do low, is two fold, and if Stormy had a clue, (he does not) he would
know why.

There is no *requirement* that heating speed be lower than cooling speed.
What is important is that you have the proper cfm per ton set up for
cooling, and that your temp rise in heating falls within the specs (temp
drop range) listed on the data plate or label in/on the furnace. Factory
default isn't necessarily what's going to be required.



No...of course not, but in the case of a furnace say..the slower of the two
speeds NORMALLY will be your heat fan speed.

I didn't doubt you for a moment, I was just clarifying because your
statement could have easily been misinterpreted as meaning that there
was some requirement for heating speed to be lower.

NORMALLY, the heating speed is lower, simply because the engineers
arranged for it to be. Lower face velocity and higher temp means less
draft and thus more comfort for the occupants. It is however less efficient.

hvacrmedic